Position measuring device

ABSTRACT

A position measuring system that includes a scale graduation, a scanning unit for scanning the scale graduation. An adjustment device that includes a displacement element for setting a position of the scanning unit with respect to the scale graduation and a gear-down mechanism arranged between the displacement element and the scanning unit, the gear-down mechanism converts a displacement movement of the displacement element into a shorter displacement movement of the scanning unit. The gear-down mechanism includes a lever arrangement with joints, which converts the displacement movement of the displacement element into a linear displacement movement of the scanning unit in relation to the scale graduation.

Applicant claims, under 35 U.S.C. §§ 120 and 365, the benefit ofpriority of the filing date of Sep. 11, 2001 of a Patent CooperationTreaty patent application, copy attached, Ser. No. PCT/EP01/10472, filedon the aforementioned date, the entire contents of which areincorporated herein by reference, wherein Patent Cooperation Treatypatent application Ser. No. PCT/EP01/10472 was not published under PCTArticle 21(2) in English.

Applicant claims, under 35 U.S.C. § 119, the benefit of priority of thefiling date of Sep. 20, 2000 of a German patent application, copyattached, Ser. No. 100 46 818.7, filed on the aforementioned date, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1 Field of the Invention

The present invention relates to a position measuring system.

2 Description of the Related Art

Such a position measuring system is known from DE 43 17 022 C1. Theposition of a scanning unit with respect to a graduated disk is adjustedby a displacement element of an adjustment device in that thedisplacement element in the form of a screw acts on a lever of areduction mechanism and displaces the scanning unit in a geared-downmanner. This displacement movement is a pivot movement around a flexiblejoint of the adjustment device.

In accordance with DE 28 44 066 A1 and DE 40 01 848 C1, the displacementalso takes place by a lever which pivots the scanning unit around aflexible joint.

However, linear displacement movements of the scanning unit with respectto the scale graduation are demanded in actual use, such as has beenexplained in EP 0 158 066 A1, for example. For adjusting fourphotoelectric barriers, which are arranged spatially offset with respectto each other, of a scanning unit of an angle measuring system, thescanning unit can be displaced in the radial direction via elongatedholes. There, the radial displacement is called parallel displacementand takes place by two elongated holes. However, a fine adjustment isnot possible with this.

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore an object of the present invention to disclose aposition measuring system with an adjustment device, by which thescanning device can be linearly displaced with respect to the scalegraduation in a highly accurate manner.

In accordance with the present invention, this object is attained by aposition measuring system that includes a scale graduation, a scanningunit for scanning the scale graduation. An adjustment device thatincludes a displacement element for setting a position of the scanningunit with respect to the scale graduation and a gear-down mechanismarranged between the displacement element and the scanning unit, thegear-down mechanism converts a displacement movement of the displacementelement into a shorter displacement movement of the scanning unit. Thegear-down mechanism includes a lever arrangement with joints, whichconverts the displacement movement of the displacement element into alinear displacement movement of the scanning unit in relation to thescale graduation.

The advantage obtained by the present invention lies in that thescanning unit can be linearly displaced in a highly accurate manner by asimple device. The displacement movement of a displacement element isconverted in a geared-down manner into a linear displacement movement,by which a delicate setting is made possible. Moreover, it is possibleto provide a reduced structural size.

The present invention will be explained in still greater detail in whatfollows by exemplary embodiments. Shown are in:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a view from above of an embodiment of an angle measuringsystem with an adjustment device in accordance with the presentinvention;

FIG. 2 shows an enlarged representation of the adjustment device inaccordance with FIG. 1;

FIG. 3 shows the adjustment device of FIG. 1 in a further adjustingposition;

FIG. 4 shows a second embodiment of an adjustment device in accordancewith the present invention;

FIG. 5 shows a third embodiment of an adjustment device in accordancewith the present invention;

FIG. 6 shows a fourth embodiment of an adjustment device in accordancewith the present invention; and

FIG. 7 shows a fifth embodiment of an adjustment device in accordancewith the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE INVENTION

The angle measuring system in accordance with FIG. 1 includes agraduated disk 1, which is rotatably seated around the axis of rotationD. The graduated disk has an incremental angle graduation 2 as a scalegraduation, whose graduation marks are radially oriented. A scanningunit 4 is adjustably fastened on a stator 3 for measuring the rotatedposition of the graduated disk 1 with respect to the stator 3. Thescanning unit 4 is designed in a known manner, so that only the scanninggrating 5 of the scanning unit 4 is represented in FIG. 1.

The scanning unit 4 is attached to a support 16 of an adjustment device10. The adjustment device 10 has two levers 11 and 12 with stop faces11.10 and 12.10. These stop faces 11.10 and 12.10 are used in a knownmanner (DE 32 28 507 C2) for aligning the scanning unit 4 with respectto the graduated disk 1. For this purpose a centering collar 6, whichextends concentrically with respect to the axis of rotation D and onwhich the adjustment device 10 is brought into contact with the stopfaces 11.10 and 12.10, is provided on the stator 3 in which thegraduated disk 1 is seated. The diameter of the centering collar 6 issubject to tolerances, so that the radial seating of the scanning unit 4by the centering collar 6 does not always meet the demands. Forcompensating diameter tolerances of the centering collar 6, the scanningunit 4 must be displaced exclusively radially, without changing thealignment with respect to the axis of rotation D (direction R) linearly.This linear displacement is performed with the adjustment device 10 andwill be further explained by FIG. 2.

As shown on a magnified scale in FIG. 2, the adjustment device 10includes a symmetrically constructed lever mechanism, having two levers11, 12, each of which can be pivoted around a flexible joint 14, 15 by acommon displacement element 13. The flexible joints 14, 15 are arrangedbetween the support 16 of the scanning unit 4 and the levers 11, 12, andare embodied in the form of weakest point joints, so that the adjustmentdevice 10 can be manufactured in one piece.

Each one of the two levers 11, 12 has a short lever arm 11.1, 12.1 and alonger lever arm 11.2, 12.2, extending from the flexible joint 14, 15.The common displacement element 13, with which the two longer lever arms11.2, 12.2 are pivoted in opposite directions around the flexible joints14, 15, acts on the two longer lever arms 11.2, 12.2. The stop faces11.10, 12.10 are formed on the shorter lever arms 11.1, 12.1. Themovement of the displacement element 13 is converted by the two leverarms 11, 12 in a geared-down manner into an oppositely directed movementof the two stop faces 11.10, 12.10. Since the two stop faces 11.10,12.10 are kept in contact with the centering collar 6, the support 16,and therefore the scanning unit 4, moves linearly in the radialdirection R when the displacement element 13 is actuated.

It is particularly advantageous if the two lever arms 11.2, 12.2 areconnected with each other via a common yoke 17, on which thedisplacement element 13 acts. The yoke 17 connects the two long leverarms 11.2, 12.2 in one piece with each other and is designed as aflexible beam, or deformation member. The displacement element in theform of a screw 13 acts against the center of the yoke 17 and bends theyoke 17 in the radial direction R. In the process the screw 13 issupported on the support 16. The deformation of the yoke 17 causes ashortening of the yoke 17, and thus the pivoting of the two levers 11and 12 over respectively identical distances in opposite directions. Tointroduce the pivot movement into the levers 11, 12, it is advantageousif a flexible joint 18, 19 is respectively arranged between the yoke 17and the longer lever arms 11.2 and 12.2.

Once the radial position of the scanning unit 4 has been correctly setby the adjustment device 10 with the gear-down mechanism includes thelevers 11,12 and the flexible joints 14, 15, it is fixed in place on thestator 3 by a fastening mechanism, not represented. The fastening bores7, 8 provided for this are schematically represented in FIG. 2.

A displacement of the scanning unit 4 transversely to the radialdirection R is also possible by the adjustment device 10. A furtherdisplacement element 9 is provided for this purpose, which acts on oneof the two longer lever arms 11.2, 12.2 and deflects it transverselywith respect to the radial direction R. This exemplary embodiment inFIG. 3.

In FIGS. 2 and 3 the levers 11, 12 are shown by solid lines in thenon-deflected position, and by dashed lines in the deflected position,i.e. the adjusted position.

Alternatively to the yoke 17 in the form of a deformation member, thecoupling of the two levers 11, 12 can be performed by a displacementelement 130 in accordance with FIG. 4. For the pivoting of the twolevers 11, 12, they are connected with each other by the screw 130. Whenturning the screw 130, the two levers 11, 12 move in opposite directionsover identical distances.

If only one of the levers 11, 12 is to be pivoted, the screw 130 must besupported on a portion of the stator 3 (stator 3 represented in FIG. 3),or on the support 16, which is indicated by the locking ring 30.

In a manner not represented, instead of a screw, the displacementelement 13 in accordance with FIG. 3 can also be an eccentric, whoseeccentric surface is in contact with the yoke 17 for bending the latteror, for deflecting only one lever 11, 12, it can be in contact with thelatter. In the exemplary embodiment in accordance with FIG. 4, theoppositely directed displacement of the two levers 11, 12 can also beprovied by a wedge which acts simultaneously on the two levers 11, 12.

In connection with the exemplary embodiments so far explained, in thecourse of adjustment it is necessary to advance the entire adjustmentdevice 10 with the scanning unit 4 on the centering collar 6. In theexemplary embodiment explained in what follows, the adjustment device 10can be rigidly fixed in place on the stator 3 by a stationary element20, and the scanning unit 4 can be set in relation to this stationaryfixed element 20 of the adjustment device 10. For this purpose, theadjustment device 10 is aligned on the centering collar 6 by the stopfaces 11.10, 12.10 and is fixed in place. The fastening bores 27 and 28are provided for fixing the stator 3 in place.

The gear-down mechanism shown in FIGS. 5 and 6 again includes alaterally-reversed lever arrangement with two levers 11, 12, which canbe pivoted in opposite directions by a displacement element 13. Thelevers 11, 12 are hinged on the stationary element 20 via flexiblejoints 14, 15, and are connected with each other by means of a commonyoke 17. The yoke 17 again is a deformation member, on whose center thedisplacement 13 acts. With a centered bending of the deformation member,the common connection between the two levers 11, 12 is shortened, whichresults in a deflection of the two levers 11, 12 over identicaldistances in opposite directions. In this case the displacement element13 can be supported on the stator 3 or, in accordance with FIG. 6, onthe support 16.

The support 16 of the scanning unit 4 can be displaced via a gear-downmechanism in the radial direction R with respect to the stationaryelement 20, analogous to the already explained exemplary embodiments.Parts with the same function are provided with the same referencenumerals in all exemplary embodiments.

The pivot movement of the two levers 11, 12 is transmitted in ageared-down manner to the support 16 with the scanning unit 4. The pivotmovement performed by the long lever arm 11.2, 12.1 is passed on to theshorter lever arm 11.1, 12.1. The further transfer takes place byrespective guide rods 21, 22 in the form of a pushrod, one end of whichis fastened on the short lever arm 11.1, 12.1, and the other end on thesupport 16. The one end of each guide rod 21,22 is fastened via aflexible joint 23, 24 on the short lever arm 11.1, 12.1, and the otherend via a further flexible joint 25, 26 on the support 16. The guiderods 21, 22 convert the pivot movement of the two levers 11, 12 into alinear displacement movement of the support 16 exclusively in the radialdirection R. In this way the scanning unit 4 is coupled via the twofastening points in the form of flexible joints 25, 26 with the leverarrangement 11, 12 and the guide rods 21, 22. By the guide rods 21, 22the pivot movement of the levers 11, 12 is converted into a paralleldisplacement of the two fastening points.

The adjustment devices in accordance with FIGS. 5 and 6 additionallypermit an adjustment of the scanning unit in a direction transversely tothe radial direction R in that—as represented in FIG. 3—a furtherdisplacement element 9 only acts on one of the two levers 11, 12.

After an adjustment has been performed, the scanning unit 4 is fixed inplace on the stator 3. Fastening bores 7, 8 are provided for thispurpose on the support 16.

Analogously with the exemplary embodiment of FIG. 4, the two levers 11,12 can also be connected with each other by a common screw 130, asrepresented in FIG. 7.

The device in accordance with the present invention can also be employedfor adjusting the scanning unit in other straight-line movementdirections, for example for setting the scanning distance between thegraduation 2 and the scanning grating 5. Moreover, the present inventionis not limited to the described angle measuring system. In place of agraduated disk 1, the scale graduation can be merely a sector, or alinear scale. The scale graduation can be designed to be scannedphotoelectrically, capacitively, magnetically or inductively. Thegraduation can be an incremental periodic graduation or an absolutesingle-track or multi-track coding.

The invention may be embodied in other forms than those specificallydisclosed herein without departing from its spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive, and the scope of theinvention is commensurate with the appended claims rather than theforegoing description.

1. A position measuring system, comprising: a scale graduation; ascanning unit for scanning said scale graduation; an adjustment devicecomprising: a displacement element that interacts with said scanningunit so as to set a position of said scanning unit with respect to saidscale graduation; and a gear-down mechanism arranged between saiddisplacement element and said scanning unit, said gear-down mechanismconverts a displacement movement of said displacement element into ashorter displacement movement of said scanning unit, wherein saidgear-down mechanism comprises a lever arrangement with joints, whichconverts said displacement movement of said displacement element into alinear displacement movement of said scanning unit in relation to saidscale graduation.
 2. The position measuring system in accordance withclaim 1, wherein said displacement element acts simultaneously on twolevers, and each of said two levers is seated so that it is pivotablearound a flexible joint.
 3. A position measuring system comprising: ascale graduation; a scanning unit for scanning said scale graduation; anadjustment device comprising: a displacement element for setting aposition of said scanning unit with respect to said scale graduation,wherein said displacement element acts simultaneously on two levers, andeach of said two levers is seated so that it is pivotable around aflexible joint, wherein said two levers are coupled together by a yoke,on which said displacement element acts, wherein said two levers arepivoted in opposite directions when said displacement element isactuated; and a gear-down mechanism arranged between said displacementelement and said scanning unit, said gear-down mechanism converts adisplacement movement of said displacement element into a shorterdisplacement movement of said scanning unit, wherein said gear-downmechanism comprises a lever arrangement with joints, which converts saiddisplacement movement of said displacement element into a lineardisplacement movement of said scanning unit in relation to said scalegraduation.
 4. The position measuring system in accordance with claim 3,wherein said yoke is a deformation member, which is formed in one pieceon said two levers.
 5. A position measuring system, comprising: a scalegraduation; a scanning unit for scanning said scale graduation; anadjustment device comprising: a displacement element for setting aposition of said scanning unit with respect to said scale graduation; agear-down mechanism arranged between said displacement element and saidscanning unit, said gear-down mechanism converts a displacement movementof said displacement element into a shorter displacement movement ofsaid scanning unit, wherein said gear-down mechanism comprises a leverarrangement with joints, which converts said displacement movement ofsaid displacement element into a linear displacement movement of saidscanning unit in relation to said scale graduation; and stop facesspaced apart from each other, by which said scanning unit is orientedwith respect to said scale graduation, and said stop faces are displacedover said lever arrangement by a common displacement element.
 6. Theposition measuring system in accordance with claim 5, wherein said scalegraduation comprises an angle graduation, which is seated in a statorand is rotated around an axis of rotation, and a centering collar, whichextends concentrically with respect to said axis of rotation, isarranged on said stator, against which said adjustment device rests bytwo stop faces, and said lever arrangement for displacing said two stopfaces is arranged between said displacement element and said two stopfaces.
 7. The position measuring system in accordance with claim 6,wherein said lever arrangement comprises two levers, each of which canbe pivoted in opposite directions around a respective flexible joint,wherein a flexible joint of one of said two levers is arranged betweensaid scanning unit and one of said two levers.
 8. The position measuringsystem in accordance with claim 7, wherein each one of said two leverscomprises: a short lever arm extending from a respective flexible joint;and a longer lever arm extending from said respective flexible joint,wherein said displacement element acts on said longer lever arm, and oneof said two stop faces is arranged on said shorter lever arm.
 9. Theposition measuring system in accordance with claim 8, wherein saidadjustment device comprises a stationary element, to which said scanningdevice is coupled by flexible joints, and said flexible joints aredisplaced parallel to each other on said scanning unit by said leverarrangement.
 10. The position measuring system in accordance with claim9, wherein said lever arrangement comprises two levers, wherewithrespectively one of said two levers acts on one of said flexible jointsof said scanning unit, and said two levers are pivoted together via saiddisplacement element.
 11. The position measuring system in accordancewith claim 10, wherein said two levers are coupled to a guide rod, whichconverts pivot movement of said two levers into a parallel movement ofsaid flexible joints of said scanning unit.
 12. The position measuringsystem in accordance with claim 11, wherein said guide rod is coupled tosaid scanning unit by one of said flexible joint, and said flexiblejoint is coupled to one of said two levers by a further flexible joint.13. A position measuring system, comprising: a scale graduation; ascanning unit for scanning said scale graduation, wherein said scanningunit generates a signal representative of a position of said scalegraduation that is scanned by said scanning unit; an adjustment devicecomprising: a displacement element for setting a position of saidscanning unit with respect to said scale graduation; and a near-downmechanism arranged between said displacement element and said scanningunit, said gear-down mechanism converts a displacement movement of saiddisplacement element into a shorter displacement movement of saidscanning unit, wherein said gear-down mechanism comprises a leverarrangement with joints, which converts said displacement movement ofsaid displacement element into a linear displacement movement of saidscanning unit in relation to said scale graduation.
 14. A positionmeasuring system, comprising: a scale graduation, a scanning unit forscanning said scale graduation, wherein said scanning unit generates asignal representative of a position of said scale graduation that isscanned by said scanning unit; an adjustment device comprising: adisplacement element for setting a position of said scanning unit withrespect to said scale graduation, wherein said displacement element actssimultaneously on two levers, and each of said two levers is seated sothat it is pivotable around a flexible joint; and a gear-down mechanismarranged between said displacement element and said scanning unit, saidgear-down mechanism converts a displacement movement of saiddisplacement element into a shorter displacement movement of saidscanning unit, wherein said gear-down mechanism comprises a leverarrangement with joints, which converts said displacement movement ofsaid displacement element into a linear displacement movement of saidscanning unit in relation to said scale graduation.
 15. The positionmeasuring system in accordance with claim 5, wherein said scanning unitgenerates a signal representative of a position of said scale graduationthat is scanned by said scanning unit.